Advances in wireless access schemes and wireless networks for cellular mobile communication (hereinafter designated “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access (EUTRA)”) have been standardized in the 3rd Generation Partnership Project (3GPP). With LTE, a multi-carrier transmission, orthogonal frequency-division multiplexing (OFDM) scheme is used as the communication scheme for wireless communication from a base station device to a mobile station device (hereinafter designated downlink or DL). Also, with LTE, a single-carrier transmission, single-carrier frequency-division multiple access (SC-FDMA) scheme is used as the communication scheme for wireless communication from a mobile station device to a base station device (hereinafter designated uplink or UL). With LTE, a discrete Fourier transform-spread OFDM (DFT-Spread OFDM) scheme is used as the SC-FDMA scheme.
With 3GPP, wireless access schemes and wireless networks that achieve even faster data communication over LTE (hereinafter designated Long Term Evolution-Advanced (LTE-A) or Advanced Evolved Universal Terrestrial Radio Access (A-EUTRA)) are being investigated. With LTE-A, the satisfaction of backward compatibility with LTE is demanded. There is demand for LTE-A to satisfy a base station device compatible with LTE-A simultaneously communicating with both mobile station devices compatible with LTE-A and mobile station devices compatible with LTE, as well as a mobile station device compatible with LTE-A communicating with a base station device compatible with LTE-A and a base station device compatible with LTE. In order to satisfy such demand, support of at least the same channel structure as LTE in LTE-A is being investigated. A channel means a medium used to transmit a signal. A channel used in the physical layer is designated a physical channel, while a channel used in the media access control (MAC) layer is designated a logical channel. Types of physical channels include the physical downlink shared channel (PDSCH) used to transmit and receive downlink data and control information, the physical downlink control channel (PDCCH) used to transmit and receive downlink control information, the physical uplink shared channel (PUSCH) used to transmit and receive uplink data and control information, the physical uplink control channel (PUCCH) used to transmit and receive control information, the synchronization channel (SCH) used to establish downlink synchronization, the physical random access channel (PRACH) used to establish uplink synchronization, the physical broadcast channel (PBCH) used to transmit downlink system information, and the like. A mobile station device or base station device places and transmits signals generated from control information, data, and the like on respective physical channels. Data transmitted on the physical downlink shared channel or the physical uplink shared channel is designated a transport block.
Control information placed on the physical uplink control channel is designated uplink control information (UCI). Uplink control information includes control information (a receive confirmation acknowledgement; ACK/NACK) indicating a positive acknowledgement (ACK) or a negative acknowledgement (NACK) with respect to received data placed on a physical downlink shared channel, control information (a scheduling request (SR)) indicating a request for the allocation of uplink resources, and/or control information (channel quality indicator (CQI)) indicating downlink reception quality (also designated the channel quality).
<Cooperative Communication>
With A-EUTRA, in order to reduce or suppress interference with respect to a mobile station device in a cell edge area, or in order to boost the reception signal power, inter-cell cooperative multipoint communication (CoMP communication) in which neighboring cells communicate cooperatively with each other is being investigated. For example, a “cell” designates a form by which a base station device communicates using an arbitrary single frequency band. For example, a method in which a weighting signal process (precoding process) that differs among multiple cells is applied to a signal, and multiple base station devices transmit the signal to the same mobile station device cooperatively (also designated joint processing or joint transmission) and the like is being investigated as inter-cell cooperative multipoint communication. With this method, the signal to interference plus noise power ratio of a mobile station device may be raised, and the reception properties in a mobile station device may be improved.
Note that for the multiple cells used in cooperative communication, different cells may be configured by different base station devices, different cells may be configured by separate remote radio heads (RRH, an outdoor radio unit smaller than a base station device; also called a remote radio unit (RRU)) managed by the same base station device, different cells may be configured by a base station device and RRHs managed by that base station device, or different cells may be managed by a base station device and RRHs managed by a base station device different from that base station device.
A base station device with wide coverage is generally designated a macro base station device. A base station device with narrow coverage is generally designated a pico base station device or a femto base station device. RRHs are generally being investigated for operation in areas of narrower coverage than macro base station devices. A deployment such as a communication system made up of a macro base station device and an RRH, and in which the coverage supported by the macro base station device includes all or part of the coverage supported by the RRH, is designated a heterogeneous network deployment. In a communication system with such a heterogeneous network deployment, a method in which the macro base station device and the RRH cooperate to transmit a signal to a mobile station device positioned in a mutually overlapping coverage area is being investigated. Herein, the RRH is managed by, and transmitting/receiving is controlled by, the macro base station device. Note that the macro base station device and the RRH are connected by a wired link such as optical fiber, and/or by a wireless link using relay technology. In this way, by having a macro base station device and an RRH respectively use all or part of the same radio resource to execute cooperative communication, overall frequency utilization efficiency (transmission capacity) may be raised within the area of coverage constructed by the macro base station device.
In the case of being positioned near a macro base station device or an RRH, a mobile station device is able to conduct single-cell communication with the macro base station device or RRH. In other words, a given mobile station device communicates with a macro base station device or RRH without using cooperative communication, and transmits or receives a signal. Furthermore, in the case the mobile station device is positioned near the edge of coverage constructed by the RRH (a cell edge), provision against co-channel interference from the macro base station device becomes necessary. For multi-cell communication (cooperative communication) between a macro base station device and an RRH, a method that reduces or suppresses interference with respect to a mobile station device in a cell edge area by using a CoMP scheme in which neighboring base stations cooperate with each other is being investigated.
Regarding the receive processing of a data signal at a mobile station device, it is necessary to acquire control information indicating the modulation scheme, the code rate, the number of spatially-multiplexed streams, the transmission power adjustment value, resource allocation, and the like. With A-EUTRA, a method of improving the capacity and/or coverage of control information regarding a data signal using cooperative communication is being investigated (NPL 1). In other words, improvement in the reception properties of control information regarding a data signal using cooperative communication is being investigated. For example, the application of cooperative communication to control information regarding a data signal using cooperative communication as well is being investigated. Specifically, there is investigation of multiple base station devices and multiple RRUs compatible with A-EUTRA applying a precoding process (beamforming process) to a signal including control information, also applying the same precoding process (beamforming process) to a reference signal (RS) for demodulating that control information, placing that signal including control information, and that RS, in a resource region in which a PDSCH is placed in EUTRA, and transmitting a signal. There is also investigation of a mobile station device compatible with A-EUTRA using a received RS that has been subjected to a precoding process to demodulate a signal including control information that has been subjected to the same precoding process, and acquiring control information transmitted by cooperative communication. This method eliminates the need for a base station device and a mobile station device to exchange information related to the precoding process applied to a signal including control information.